Is Leaving Hair Oils Overnight Safe?

• Oils such as such as castor oil, argan oil, and rosemary oil can be used to nourish the hair, reduce frizz, and enhance shine. 
• If you’re going to use hair oil, as a rule of thumb, experts say people with dry hair should apply it two to three times per week. People with oily hair should stick to once per week.
• While it’s generally safe to leave oils in your hair overnight, overuse may lead to irritation, redness, or flakiness. 

Of the endless haircare items that promise to boost moisture, add shine, and tame frizz, a go-to type of product currently embraced by beauty bloggers and hairstylists alike is hair oil.

Different types of hair oil have different uses, but generally, they are formulated to nourish, hydrate, and improve the overall health of hair, Yoram Harth, MD, a board-certified dermatologist and Medical Director of MDhair.

To use hair oil, you typically massage a small amount into your scalp, then massage more oil through sections of hair from root to tip. While your hair can reap benefits from this process in just a few hours, some people choose to leave it in overnight for maximum effectiveness.

But is that a good idea? Here’s what you need to know and why it depends on the oil.

What Kinds of Oils Can You Use on Your Hair? 

The kind of oil you choose should depend on your specific hair needs and the outcome you hope to achieve, Harth said. Oils are generally used for cosmetic reasons like adding luster or reducing frizz, though some can help with scalp conditions. For the most part, serums are used to treat the skin of the scalp, addressing issues like dryness, flakiness, and irritation.

“Hair oils can be used for cosmetic benefits, improving hair’s overall texture and appearance, while scalp serums may contain therapeutic properties to assist in hair growth and scalp health maintenance,” said Harth.

According to Marisa Garshick, MD, FAAD, a board-certified dermatologist at MDCS Dermatology, the main types of hair oil include: 

• Argan oil: Argan oil is rich in omega-3 fatty acids, antioxidants, and hydrating properties, making it a good choice for moisturizing and softening hair. It can also help with frizz control and add shine.
• Castor oil: Castor oil is high in vitamin E and contains ricinoleic acid, a type of fatty acid that can boost circulation in the scalp. Subsequently, it promotes healthier and stronger hair, contributing to more shine.
• Coconut oil: Coconut oil is rich in fatty acids such as lauric acid, which can help with moisturization if you have dry hair. It may also be used to improve hair texture or help manage a dry, itchy scalp.
• Jojoba oil: Jojoba oil contains many vitamins, such as vitamins A, B, and E. Because it is lightweight and easily absorbed, it’s a good choice for people with fine hair or oily hair.
• Rosemary oil: Rosemary oil can reduce hair damage and breakage, making hair appear stronger. In addition to its antibacterial and antimicrobial properties, rosemary oil is also anti-inflammatory, which can help to reduce scalp redness, irritation, and even dandruff. It may also promote hair growth by stimulating hair follicles.

While anyone can use hair oil, people with fine or oily hair—or those prone to acne or folliculitis of the scalp—should be cautious and specifically seek out an oil specific to their hair or scalp type. 

“People with sensitive skin should always be cautious when using a hair oil, as with any new product that is added to a routine,” said Garshick.

When to Dilute Your Oil

Most hair oils on the market are already diluted or mixed with ingredients to reduce their potency. But if you purchase a 100% pure essential oil (like Rosemary oil), consider diluting it with a lighter oil, such as coconut or jojoba, in order to avoid irritation. You can also mix it into your shampoo or conditioner.

Can You Leave Hair Oil in Overnight?

Using oils in your hair overnight is generally safe and can offer various benefits, such as deeper penetration of the oil in the scalp, hydration, and nourishment. But this may not be suitable for all hair types or for those with a sensitive scalp, Anna Chacon, MD, a board-certified dermatologist at Miami Derm.

“Prolonged oil use can lead to buildup and greasiness. Those with fine or oily hair should use them sparingly as they can weigh down the hair or make it overly greasy,” said Chacon. “People with dry or damaged hair can benefit more from regular use.”

The frequency of applying nighttime hair oils will vary from person to person and will depend on your hair type and the specific oil’s properties. As a rule of thumb, Chacon recommends people with dry hair use oil two to three times per week. For people with oily hair, once a week may be sufficient.

If you decide to use oil overnight, Chacon suggests washing it out the next morning to prevent excess build-up of the product and prevent issues like clogged pores.

Do a ‘Patch Test’ First

Although using oil on your hair is generally safe, it’s important to be aware that hair oils can cause potential side effects, celebrity hairstylist Chaz Dean, founder of WEN Hair & Body Care. 

Oils may cause scalp irritation, allergic reactions, redness, itchiness, or flakiness, especially for people with sensitive skin.

To avoid potential reactions or side effects, Dean recommends doing a patch test on a small part of your skin before applying any oil for the first time. If you notice a reaction, you may have a sensitivity or allergy to an ingredient in the oil.

Takeaway Note

Anyone can use a hair oil, but choosing one and determining how often to use it depends on your hair type, personal sensitives, and hair care needs. Depending on the oil and treatment goal, leaving hair oil on overnight is an option, but experts generally recommend rinsing it off in the morning.